Logic Inverter with Schmitt Trigger

This circuit can take noisy active low input signal, invert the logic and provide clean Schmitt Trigger output.

Soft-Start and Protection Circuit

When the input is below 18 V, Q1 is OFF state allowing C3 to be charged though R3. Thus turning on Q105. Once the input voltage exceed 18 plus two diode drop Volts, Q1 will turn on that discharge C3 and Q105 is OFF.

Once the input goes back below 18 V, Q1 is turn off again. This allows C3 to be charged slowly resulting soft-start at the output.

Pulse Width Stretcher using 555 Timer IC

This circuit will invert and stretch the short period active low input signal as below.

Required pulse width can be calculated by using this equation.

Micro-controller Output Protection by Current Limiting

Q1B is the pass or output transistor. R2 sense the output current. Q1A  is the protection transistor which turns on as soon as the voltage across R2 becomes about 0.65 V.
Maximum current = VBE,Q1A / R2 = 0.65 / 33 = 19.7 mA

High Voltage Monitoring/ Measuring using Microcontroller's ADC input

Voltage divider resistor network is used to step monitored voltage down to the range as necessary  for A/D conversion. Passive low-pass filter is used for noise rejection.

Voltage Doubler Circuit

This circuit will convert AC voltage to large DC output voltage. It will take AC input, convert it to DC and double the voltage to the output.

Reverse Polarity Protection

VGS (th) , Gate Source threshold voltage = -2.0 V
Zener Voltage = 10 V, Q1-VGS max = +/- 20V 
Zener diode, D3 will protect the gate from excessive voltages/ unwanted spikes

By referring the Gate signal to the ground line, the device is fully turned on when the battery is applied in the right polarity. For the first start up, the intrinsic body diode of the MOSFET will conduct, until the channel is switched on in parallel. The Zener diode will clamp the Gate of the MOSFET to its Zener voltage and protecting it against overvoltage. By reverse polarity, the MOSFET will be switched off, because the Gate Source voltage for this case will be positive (voltage drop over the Zener diode). 

Logic Input/ Push Button input Buffer Circuit

This circuit squares up and debounces a push button or logic input signal.

Bi-directional Logic Level Shifter

VGS (th) = 1.3 V (Threshold Voltage)
Input = 0V ; VGS > VGS(th) ; FET = ON ; Output = 0V
Input = 3.3V ; VGS < VGS(th) ; FET = OFF ; Output = 5V

Protecting microcontroller's Inputs

1) Filtering

This circuit can be used to protect I/Os of micro-controller/ processors.  D1A is used for Transient Voltage Suppression or ESD protection. R1 acts as current limiting resister as well as low pass filter together with C1. The value of the resistor and the capacitor must be sized so that the micro-controller does not miss any signals.

Rise time of the fastest income edge = 2.2 RC

2) Limiting Current

This circuit limit the input current to 23.2 mA (VZ/R1 = 5.1 / 220).

3) Limiting Voltage

Use schottky diodes with 0.2 Vf for better performance. Once the voltage at I/O pin is greater than VCC by about 0.2V, the top diode will start to conduct. The bottom diode will conduct for voltage less than -0.2V.

Embedded C Programming For PIC Chips

C Programming Using CCS Compiler For PIC Microcontrollers

Here is a link for good tutorial of programming PIC microcontroller in C.

http://harfordhackerspace.org/2010/02/programming-pic-microcontrollers-in-c/

Motor Control using Pulse-Width Modulation (PWM)


In this program, a jumper on Port B directly selects the PWM output. PWM output is only present if a jumper to ground is present on one the least significant 3 bits of port B.



The program demonstrates the use of control registers to effect PWM operation.  One thing to notice is the fact that the program waits for a change on the input pins before selecting a new pulse-width duty cycle and reloading CCPR1.